Effect of cobalt-mediated Toll-like receptor 4 activation on inflammatory responses in endothelial cells

Abstract

Cobalt-containing metal-on-metal hip replacements are associated with adverse reactions to metal debris (ARMD), including inflammatory pseudotumours, osteolysis, and aseptic implant loosening. The exact cellular and molecular mechanisms leading to these responses are unknown. Cobaltions (Co2+) activate human Toll-like receptor 4 (TLR4), an innate immune receptor responsible for inflammatory responses to Gram negative bacterial lipopolysaccharide (LPS).We investigated the effect of Co2+-mediated TLR4 activation on human microvascular endothelial cells (HMEC-1), focusing on the secretion of key inflammatory cytokines and expression of adhesion molecules. We also studied the role of TLR4 in Co2+-mediated adhesion molecule expression in MonoMac 6 macrophages.We show that Co2+ increases secretion of inflammatory cytokines, including IL-6 and IL-8, in HMEC-1. The effects are TLR4-dependent as they can be prevented with a small molecule TLR4 antagonist. Increased TLR4-dependent expression of intercellular adhesion molecule 1 (ICAM1) was also observed in endothelial cells and macrophages. Furthermore, we demonstrate for the first time that Co2+ activation of TLR4 upregulates secretion of a soluble adhesion molecule, sICAM-1, in both endothelial cells and macrophages. Although sICAM-1 can be generated through activity of matrix metalloproteinase-9 (MMP-9), we did not find any changes in MMP9 expression following Co2+ stimulation.In summary we show that Co2+ can induce endothelial inflammation via activation of TLR4. We also identify a role for TLR4 in Co2+-mediated changes in adhesion molecule expression. Finally, sICAM-1 is a novel target for further investigation in ARMD studies.

Increased Systemic Malondialdehyde Levels and Decreased Mo/Co, Co/Fe2+ Ratios in Patients with Long-Term Dental Titanium Implants and Amalgams

“…Since Mo decreased among A + I participants and their cobalt (Co) levels rose, we cannot exclude the possibility that systemic malondialdehyde (MDA) levels could indirectly reflect enhanced susceptibility to oxidative stress among A + I patients. In addition, Co induces inflammatory responses via TLR-4 activation in culture cells, responses which are abolished by blocking TLR-4 receptors [33]. In agreement with this hypothesis, we detected lower Mo/Co and Mo/Fe 2+ ratios in the (A + I) group than in those with long-term dental amalgams only (A); The low Mo/Co ratio (A + I) suggests a Mo deficit in patients with long-term implants and amalgams (A + I) although Mo levels were similar to controls in patients with long-term amalgams alone.…”

Blood cytokine pattern and clinical outcome in knee arthroplasty patients: comparative analysis 5 years after standard versus “hypoallergenic” surface coated prosthesis implantation

“…Recent investigations have shown that cobalt and nickel induce such IL-8 expression via TLR4 activation (Anjum et al. 2016, Lin et al. 2016).…”

“…With regard to prolonged peri-implant inflammatory response, Anjum et al. (2016) presented an interesting working model. Cobalt ions released from arthroplasty activate TLR4 on immune cells and endothelial cells, resulting in cytokine and chemokine (including IL-8) release that leads among others to inflammatory cell recruitment from the circulation.…”

Heparanase-2 protects from endothelial injury by inhibiting TLR4 signaling

“…1E). IL-6 was selected as a readout of the LPS-induced TLR4 response because IL-6 expression in endothelial cells was shown to be TLR4dependent 36 . In our experiments, the LPS-dependent expression of IL-6 was abrogated by the TLR4 inhibitor Cli-095 (data not shown).…”